The present invention relates to an implantable device for the administration of active substances to plants. Administering active substances to plants by means of implantable devices is known per se and is mentioned in the relevant literature. For example, patent documents JP 58-39602 and AU 84 31497 describe such devices.
The publication JP 58-39602 discloses implantable, swellable active substance systems consisting of a mixture of hydrophilic and water-absorbing polymers. The operating principle of these systems consists in the fact that the release of the active substance is effected as a result of its solubilization and is therefore controlled by the water absorption of the plant. However, this controlling mechanism has the following disadvantage: Since the active substance is released according to the water absorption, the release rates are determined by the hydration state of the plant's tissue cells at the site of application. Previous experience has shown that the degree of cell hydration is subject to great variations, and that the extent of these variations depends on the water balance state of the plant. Extremely low or extremely high water potentials of the plant cells can result either in an interruption of the active substance release or in a rapid release involving an undesired premature exhaustion of the system. A long-term and reliable control of the active substance amount to be released per time unit is not possible with these systems.
The patent AU 843 1497 relates to a release system primarily developed for irrigation and fertilization purposes. It consists of a porous ceramic implant and an external gas or liquid reservoir which are connected with each other. In this case water and active substance are supplied by utilizing the capillary forces of the implant body, the natural transpiration flow of the plant representing the driving power required to transport the active substance carrier liquid. So, both liquid flow and active substance supply to the conductive system of the plant are controlled by the plant itself. For this reason, this system is unsuitable for an exact active substance dosage, rendering the administration of plant protection agents or growth regulators impossible. In forest and horticultural crop protection it is important to adapt the active substance demand to the specific requirements of the respective host-pathogen-relation (time-dependent development of disease and pest attack, extent of the economic damage threshold). The active substance release rate is not the last factor which influences the cost situation in the treatment of a larger stock of plants or trees, for example.